Jan Wieck <[EMAIL PROTECTED]> writes:I checked the background writer for this and I can not reproduce the behaviour. If the bgwriter had zero blocks to write it does PG_USLEEP for 10 seconds, which on Unix is done by select() and that is correctly interrupted when the postmaster sends it the term signal on shutdown.
This appears to be a platform-dependent behavior. The HPUX select(2) man page says
[EINTR] The select() function was interrupted before any of the selected events occurred and before the timeout interval expired. If SA_RESTART has been set for the interrupting signal, it is implementation-dependent whether select() restarts or returns with EINTR.
which text also appears verbatim in the Single Unix Spec. Since we set SA_RESTART for every signal except SIGALRM (see pqsignal.c), we are subject to the implementation dependency for SIGTERM.
That explains it.
Tracing the bgwriter process on my machine makes it real obvious that in fact the select delay is allowed to finish out when SIGTERM is received. In fact worse than that: it's restarted from the beginning. If 5 seconds have already elapsed, another 10 still elapse before the select exits.
This won't do :-(. We cannot afford to fritter away 10 seconds in the SIGTERM shutdown cycle --- on typical systems init isn't going to give us more than 20 seconds before a hard kill.
I'd suggest reducing the delay to a second or two, or perhaps breaking it into several 1-second waits with interrupt flag checks between.
In the longer run we might want to rethink what we are doing with SA_RESTART, but I am not sure about the implications of fooling with that.
I think we should at this point have some maximum value for PG_xSLEEP over which it falls back to a function call that does either this breaking up into a loop with checking InterruptPending or removes the SA_RESTART flag while wating for the timeout.
Jan
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